We've got the builders in adding a two storey extension to our
Bradstone house.

Question. They've done the footings and their doing the blockwork for
the inner skin. However, they aren't tying it into the existing
walls. They're putting in plenty of wall ties to join the inner to
the outer skin, and the chief brickie assures me that he's going to
tie in the outer skin by interleaving alternate courses. Will this
suffice to make the walls sufficiently robust? Or should I ask him to
tie in the inner skin as well?

TIA

Edward